Voltage level shifting circuit and method

ABSTRACT

A voltage level shifting circuit and method that can be used for shifting the voltage level of an input signal to provide an output signal having a higher output voltage level. The voltage level shifting circuit includes pull-up transistors that are switched OFF by the voltage of a pair of switching nodes and not the voltage at the output node. The speed at which the pull-up transistors can be switched OFF is decoupled to some extent from the speed at which the voltage at the output node changes. Additionally, having the output node separated from the nodes that switch the pull-up transistors OFF further allows for dimensions of the various transistors of the voltage level shifting circuit to be scaled advantageously.

TECHNICAL FIELD

The present invention relates to voltage level shifting circuits, andmore particularly, to a voltage level shifting circuit and method thatcan be used for shifting the voltage level of an input signal to providean output signal having a higher output voltage level where thedifference between the voltage levels of the input and output signals islarge.

BACKGROUND OF THE INVENTION

FIG. 1 illustrates a conventional voltage level shifting circuit 100 fortranslating an input signal IN having an input voltage level V1 to anoutput signal OUT having an output voltage level V2. The voltage levelshifting circuit 100 includes p-channel MOS (PMOS) pull-up transistors104 and 108 coupled to a voltage supply providing the voltage level V2.Coupled to the PMOS pull-up transistors 104, 108 are PMOS loadtransistors 120, 124 and n-channel MOS (NMOS) pull-down transistors 112,116, all respectively. Gates of the PMOS load transistors 120, 124 andof the NMOS pull-down transistors 112, 116 are coupled to receive the INsignal having the V1 voltage level through series coupled inverters 150,154. The OUT signal having the V2 voltage level is provided at an outputnode 134.

In operation, a falling edge of the IN signal causes the NMOS pull-downtransistor 112 and the PMOS load transistor 124 to switch ON, and theNMOS pull-down transistor 116 and the PMOS load transistor 120 to switchOFF. In this state, the gate of the PMOS pull-up transistor 108 iscoupled to ground, switching ON the PMOS pull-up transistor 108. Withboth the PMOS pull-up transistor 108 and the PMOS load transistor 124switched ON, the output node is coupled to the V2 voltage supply. Inresponse to a rising edge of the IN signal, the PMOS load transistor 120and the NMOS pull-down transistor 116 are switched ON, and the PMOS loadtransistor 124 and the NMOS pull-down transistor 112 are switched OFF.As a result, the output node 134 is coupled to ground through the NMOSpull-down transistor 116. As the voltage of the output node 134 ispulled to ground, the PMOS pull-up transistor 104 eventually switches ONto couple the gate of the PMOS pull-up transistor 108 to the V2 voltagesupply 106, thereby switching OFF the PMOS pull-up transistor 108 anddecoupling the output node 134 from the V2 voltage supply 106. When theoutput node 134 is decoupled from the V2 voltage supply 106, the voltageof the output node 134 is finally pulled to ground.

The performance of the conventional voltage level shifting circuit 100begins to suffer as the voltage difference between the input and outputsignals becomes greater. That is, the voltage difference between theinput and output signals affects the speed at which the PMOS pull-uptransistors 104, 108 and PMOS load transistors 120, 124 switch OFF,which in turn, specifically with respect to the PMOS pull-up transistor108 and the PMOS load transistor 124, directly affects the speed atwhich the voltage at the output node 134 can be pulled to ground.

As previously described, a rising edge of the IN signal causes the NMOSpull-down transistor 116 to switch ON, thereby coupling the output node134 to ground. However, at this time, the PMOS pull-up transistor 108and the PMOS load transistor 124 are still ON because the thresholdvoltages for both transistors are still exceeded. With a large voltagedifference between the V2 voltage level and the V1 voltage level, alarge voltage swing must occur before the voltage at the gates of thePMOS pull-transistor 108 and the PMOS load transistor 124 relative tothe voltage at the sources of the two transistors will decrease belowthe respective threshold voltages to switch the transistors OFF. Beforethe PMOS pull-up transistor 108 and the PMOS load transistor 124 areswitched OFF, it is difficult for the NMOS pull-down transistor 116 topull the output node LOW and because current is sunk through the NMOSpull-down transistor 116 to ground, power consumption is high. Finally,when the voltage of the output node 134 decreases enough so that thethreshold voltage of the PMOS pull-up transistor 104 is exceeded,switching OFF the PMOS pull-up transistor 108 is accelerated due to thecoupling of its gate to the V2 voltage supply. Although the PMOS loadtransistors 120 and 124 can be used to mitigate the problem by havingdevice dimensions that can lower the voltage at the output node 134, aswell as limit the current consumption, the current drive capability ofthe voltage level shifting circuit 100 is compromised as a result.

SUMMARY OF THE INVENTION

The present invention is directed to a voltage level shifting circuitand method for shifting the voltage level of an input signal and providean output signal having a higher output voltage level. In one aspect ofthe invention, the voltage level shifting circuit includes a firstcurrent path from a voltage supply to ground having a first input signalnode to which an input signal is coupled, a first output signal nodefrom which an output signal is provided, a first pull-up node, and afirst switching node. The first discharge path couples the voltagesupply to the first output signal node under control of the firstpull-up node and couples the switching node to ground in response to theinput signal. The voltage level shifting circuit further includes asecond current path from the voltage supply to ground having a secondinput signal node to which a complementary input signal is coupled, asecond output signal node from which a complementary output signalprovided, a second pull-up node coupled to the first switching node, anda second switching node coupled to the first pull-up node. The seconddischarge path couples the voltage supply to the second output signalnode under control of the second pull-up node and couples the secondswitching node to ground in response to the complementary input signal.A third current path is included in the voltage level shifting circuitto couple the output signal node to ground in response to the inputsignal.

In another aspect of the present invention, a voltage level of an inputsignal is shifted to an output voltage level by coupling an output nodeto a voltage supply providing the output voltage level in response to aninput signal having a first voltage level in order to provide an outputsignal having the output voltage level. Additionally, a first switchingnode is coupled to ground in response to the input signal having asecond voltage level and a second switching node is coupled to thevoltage supply in response to the first switching node coupled toground. The output node is further coupled to ground in response to theinput signal having a second voltage level, and the first switching nodeis decoupled from the output node in response to the input signal havinga second voltage level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a conventional voltage level shiftingcircuit.

FIG. 2 is a schematic drawing of a voltage level shifting circuitaccording to an embodiment of the present invention.

FIG. 3 is a schematic drawing of a voltage level shifting circuitaccording to another embodiment of the present invention.

FIG. 4 is a partial functional block diagram illustrating a memorydevice including a voltage level shifting circuit according to anembodiment of the present invention.

FIG. 5 is a partial functional block diagram illustrating aprocessor-based system including the memory device of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention are directed to voltage levelshifting circuits and methods that can be used for shifting the voltagelevel of an input signal to provide an output signal having a higheroutput voltage level where the difference between the voltage levels ofthe input and output signals is large. Certain details are set forthbelow to provide a sufficient understanding of the invention. However,it will be clear to one skilled in the art that the invention may bepracticed without these particular details. In other instances,well-known circuits, control signals, and timing protocols have not beenshown in detail in order to avoid unnecessarily obscuring the invention.

FIG. 2 illustrates a voltage level shifting circuit 200 according to anembodiment of the present invention. The voltage level shifting circuit200 translates an input signal IN having an input voltage level V1 to anoutput signal OUT having an output voltage level V2. The voltage levelshifting circuit 200 includes pull-up transistors 204 and 208 coupled toa voltage supply providing the V2 voltage. The gates of the pull-uptransistors 204 and 208 are coupled to switching nodes 210 and 206,respectively. The switching nodes can be coupled to ground throughswitching transistors 212, 216. Coupling transistors 220 and 224 arecoupled between the pull-up transistors 204 and 208 and the switchingnodes 206 and 210, all respectively. The IN signal is provided to thevoltage level shifting circuit 200 through series coupled inverters 150and 154. More specifically, the gates of the coupling transistor 220 andthe switching transistor 212 are coupled to the output of the inverter150 to receive an inverted IN signal, and the gates of the couplingtransistor 224 and the switching transistor 216 are coupled to theoutput of the inverter 154 to receive a twice inverted IN signal (i.e.,inverted once through the inverter 150 and inverted again through theinverter 154). The voltage level shifting circuit 200 further includesdischarge transistor 230 coupled to an output node 234 and ground. TheOUT signal is provided from the output node 234. The gate of thedischarge transistor 230 is coupled to the output of the inverter 154.As will be discussed in more detail below, the discharge transistor 230assists in pulling the voltage of the output node 234 to ground toincrease responsiveness of the voltage level shifting circuit 200.

In operation, a falling edge of the IN signal is inverted by theinverter 150 to a rising edge signal that switches OFF the couplingtransistor 220 and switches ON the switching transistor 212. The risingedge signal output by the inverter 150 is inverted by the inverter 154into a falling edge signal that switches OFF the switching transistor216 and switches ON the coupling transistor 224. The falling edge signaloutput by the inverter 154 also switches OFF the discharging transistor230 to decouple the output node 234 from ground. In this state, theswitching node 206 is coupled to ground through the switching transistor212 to switch ON the pull-up transistor 208 and couple the output node234 to the voltage supply providing the V2 voltage. As a result, afalling edge IN signal provides a rising edge OUT signal having a V2voltage level. With the gate of the coupling transistor 224 receivingthe falling edge signal from the inverter 154, the coupling of theoutput node 234 to the voltage supply eventually switches ON thecoupling transistor 224 to couple the V2 voltage level to the gate ofthe pull-up transistor 204. In response, the pull-up transistor 204 isswitched OFF.

At a rising edge of the IN signal, the IN signal is inverted by theinverter 150 to a falling edge signal, thereby switching OFF theswitching transistor 212 and switching ON the coupling transistors 220.The falling edge signal output by the inverter 150 is inverted by theinverter 154 to a rising edge signal that switches OFF the couplingtransistor 224 and switches ON the switching transistor 216 and thedischarge transistor 230. In this state, the switching node 210 iscoupled to ground to switch ON the pull-up transistor 204. With the gateof the coupling transistor 220 coupled to a LOW voltage level at theoutput of the inverter 150, the coupling transistor 220 eventuallyswitches ON and couples the gate of the pull-up transistor 208 to thevoltage supply, thereby switching OFF the pull-up transistor 208 anddecoupling the output node 234 from the voltage supply. Concurrently,the discharge transistor 230 couples the output node 234 to ground toquickly pull the output node 234 from the V2 voltage level to a LOWvoltage level as the pull-up transistor 208 is switched OFF.

It will be appreciated that in the voltage level shifting circuit 200,the pull-up transistors 204 and 208 are not switched OFF by the voltageof the output node 234, but rather, by the voltage at the switchingnodes 210 and 206, respectively. In contrast, as previously mentioned,the voltage at the output node of a conventional voltage shiftingcircuit is used to switch OFF a pull-up transistor, as well as providean output signal while the output node is pulled to ground. Withembodiments of the present invention, the speed at which the pull-uptransistors 204 and 208 can be switched OFF is decoupled to some extentfrom the speed at which the voltage at the output node 234 changes.While the discharging transistor 230 is coupling the output node 234 toground, the switching node 206 is coupled to the voltage supply throughthe coupling transistor 220 and the pull-up transistor 204 to providesufficient voltage to quickly switch OFF the pull-up transistor 208 andthus, allow the output node 234 to be pulled to ground through thedischarging transistor 230 more quickly.

Additionally, having the output node separated from the nodes thatswitch the pull-up transistors 204, 208 ON and OFF further allow fordimensions of the various transistor to be scaled advantageously. Forexample, the dimensions of the pull-up transistors 204, 208 can beselected to provide sufficient current drive to the output node 234rather than in consideration of the rate at which the output node 234can be pulled to ground through the discharging transistor 230.Additionally, since the output node 234 is coupled to the voltage supplythrough the pull-up transistor 208, the coupling transistors 220, 224can be relatively “small” because the output current is not driventhrough the coupling transistors 220, 224 to the output node 234. Withthe smaller dimensions, the coupling transistors 220, 224 can beswitched ON quickly to couple the gate of the pull-up transistor 208 tothe voltage supply, thereby using the relatively high voltage of thevoltage supply to switch OFF the pull-up transistor 208 and increase theresponsiveness of voltage changes at the output node 234.

FIG. 3 illustrates a voltage level shifting circuit 300 according toanother embodiment of the present invention. The voltage level shiftingcircuit 300 is similar to the voltage level shifting circuit 200 of FIG.2. However, the voltage level shifting circuit 300 further includes asecond discharging transistor 332 coupled to a node 336, which can beused to provide an output signal complementary to the OUT signalprovided at the output node 334. Operation of the voltage level shiftingcircuit 300 is also to that described above with respect to the voltagelevel shifting circuit 200. However, the second discharging transistor332 is switched ON in addition to the switching transistor 312 inresponse to a rising edge signal output from the inverter 150 to quicklydischarge the node 336.

FIG. 4 illustrates a memory device 400 including at least one voltagelevel shifting circuits according to an embodiment of the presentinvention. The memory device 400 includes an address register 402 thatreceives row, column, and bank addresses over an address bus ADDR, witha memory controller (not shown) typically supplying the addresses. Theaddress register 402 receives a row address and a bank address that areapplied to a row address multiplexer 404 and bank control logic circuit406, respectively. The row address multiplexer 404 applies either therow address received from the address register 402 or a refresh rowaddress from a refresh counter 408 to a plurality of row address latchand decoders 410A-D. The bank control logic 406 activates the rowaddress latch and decoder 410A-D corresponding to either the bankaddress received from the address register 402 or a refresh bank addressfrom the refresh counter 408, and the activated row address latch anddecoder latches and decodes the received row address. Included in therow address latch and decoders 410A-D are respective voltage levelshifting circuits 411A-D for shifting the voltage of signals having afirst voltage level to an output signal having a higher second voltagelevel.

In response to the decoded row address, the activated row address latchand decoder 410A-D applies various signals to a corresponding memorybank 412A-D, including a row activation signal to activate a row ofmemory cells corresponding to the decoded row address. Each memory bank412A-D includes a memory-cell array having a plurality of memory cellsarranged in rows and columns. The row activation signal can have thesecond voltage level as provided by a respective voltage level shiftingcircuits 411A-D in order to drive the word line to a sufficiently highvoltage level to activate access transistors of the memory cells. Thedata stored in the memory cells in the activated row are sensed andamplified by sense amplifiers in the corresponding memory bank. The rowaddress multiplexer 404 applies the refresh row address from the refreshcounter 408 to the decoders 410A-D and the bank control logic circuit406 uses the refresh bank address from the refresh counter when thememory device 400 operates in an auto-refresh or self-refresh mode ofoperation in response to an auto- or self-refresh command being appliedto the memory device 400, as will be appreciated by those skilled in theart.

A column address is applied on the ADDR bus after the row and bankaddresses, and the address register 402 applies the column address to acolumn address counter and latch 414 which, in turn, latches the columnaddress and applies the latched column address to a plurality of columndecoders 416A-D. The bank control logic 406 activates the column decoder416A-D corresponding to the received bank address, and the activatedcolumn decoder decodes the applied column address. Depending on theoperating mode of the memory device 400, the column address counter andlatch 414 either directly applies the latched column address to thedecoders 416A-D, or applies a sequence of column addresses to thedecoders starting at the column address provided by the address register402. In response to the column address from the counter and latch 414,the activated column decoder 416A-D applies decode and control signalsto an I/O gating and data masking circuit 418 which, in turn, accessesmemory cells corresponding to the decoded column address in theactivated row of memory cells in the memory bank 412A-D being accessed.

During data read operations, data being read from the addressed memorycells is coupled through the I/O gating and data masking circuit 418 toa read latch 420. The I/O gating and data masking circuit 418 supplies Nbits of data to the read latch 420, which then applies two N/2 bit wordsto a multiplexer 422. In the embodiment of FIG. 3, the circuit 418provides 64 bits to the read latch 420 which, in turn, provides two 32bits words to the multiplexer 422. A data driver 424 sequentiallyreceives the N/2 bit words from the multiplexer 422 and also receives adata strobe signal DQS from a strobe signal generator 426. The DQSsignal is used by an external circuit such as a memory controller (notshown) in latching data from the memory device 400 during readoperations. The data driver 424 sequentially outputs the received N/2bits words as a corresponding data word DQ, each data word being outputin synchronism with a rising or falling edge of a CLK signal that isapplied to clock the memory device 400. The data driver 424 also outputsthe data strobe signal DQS having rising and falling edges insynchronism with rising and falling edges of the CLK signal,respectively. Each data word DQ and the data strobe signal DQScollectively define a data bus DATA.

During data write operations, an external circuit such as a memorycontroller (not shown) applies N/2 bit data words DQ, the strobe signalDQS, and corresponding data masking signals DM on the data bus DATA. Adata receiver 428 receives each DQ word and the associated DM signals,and applies these signals to input registers 430 that are clocked by theDQS signal. In response to a rising edge of the DQS signal, the inputregisters 430 latch a first N/2 bit DQ word and the associated DMsignals, and in response to a falling edge of the DQS signal the inputregisters latch the second N/2 bit DQ word and associated DM signals.The input register 430 provides the two latched N/2 bit DQ words as anN-bit word to a write FIFO and driver 432, which clocks the applied DQword and DM signals into the write FIFO and driver in response to theDQS signal. The DQ word is clocked out of the write FIFO and driver 432in response to the CLK signal, and is applied to the 1/O gating andmasking circuit 418. The I/O gating and masking circuit 418 transfersthe DQ word to the addressed memory cells in the accessed bank 412A-Dsubject to the DM signals, which may be used to selectively mask bits orgroups of bits in the DQ words (i.e., in the write data) being writtento the addressed memory cells.

A control logic and command decoder 434 receives a plurality of commandand clocking signals over a control bus CONT, typically from an externalcircuit such as a memory controller (not shown). The command signalsinclude a chip select signal CS*, a write enable signal WE*, a columnaddress strobe signal CAS*, and a row address strobe signal RAS*, whilethe clocking signals include a clock enable signal CKE* andcomplementary clock signals CLK, CLK*, with the “*” designating a signalas being active low. The command signals CS*, WE*, CAS*, and RAS* aredriven to values corresponding to a particular command, such as a read,write, or auto-refresh command in response to the clock signals CLK,CLK*, the command decoder 434 latches and decodes an applied command,and generates a sequence of clocking and control signals that controlthe components 402-432 to execute the function of the applied command.The clock enable signal CKE enables clocking of the command decoder 434by the clock signals CLK, CLK*. The command decoder 434 latches commandand address signals at positive edges of the CLK, CLK* signals (i.e.,the crossing point of CLK going high and CLK* going low), while theinput registers 430 and data drivers 424 transfer data into and from,respectively, the memory device 400 in response the data strobe signalDQS. The detailed operation of the control logic and command decoder 434in generating the control and timing signals is conventional, and thus,for the sake of brevity, will not be described in more detail. Althoughpreviously described with respect to a dynamic random access memorydevice, it will be appreciated by those ordinarily skilled in the artthat embodiments of the present invention can be utilized inapplications other than for a memory device where it is desirable toshift the voltage level of an input signal from a first voltage level toa second, higher voltage level.

FIG. 5 is a block diagram of a computer system 500 including computercircuitry 502 including the memory device 400 of FIG. 4. Typically, thecomputer circuitry 502 is coupled through address, data, and controlbuses to the memory device 400 to provide for writing data to andreading data from the memory device. The computer circuitry 502 includescircuitry for performing various computing functions, such as executingspecific software to perform specific calculations or tasks. Inaddition, the computer system 500 includes one or more input devices504, such as a keyboard or a mouse, coupled to the computer circuitry502 to allow an operator to interface with the computer system.Typically, the computer system 500 also includes one or more outputdevices 506 coupled to the computer circuitry 502, such as outputdevices typically including a printer and a video terminal. One or moredata storage devices 508 are also typically coupled to the computercircuitry 502 to store data or retrieve data from external storage media(not shown). Examples of typical storage devices 508 include hard andfloppy disks, tape cassettes, compact disk read-only (CD-ROMs) andcompact disk read-write (CD-RW) memories, and digital video disks(DVDs).

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. For example, embodiments of thepresent invention can be modified to shift the voltage level of an inputsignal having a negative voltage to a less negative voltage level or toground. Such modifications are well within the skill of those ordinarilyskilled in the art. Accordingly, the invention is not limited except asby the appended claims.

1. A voltage shifting circuit, comprising: a first current path from avoltage supply to ground, the first path having a first input signalnode to which an input signal is coupled, a first output signal nodefrom which an output signal is provided, a first pull-up node, and afirst switching node, the first discharge path coupling the voltagesupply to the first output signal node under control of the firstpull-up node and coupling the switching node to ground in response tothe input signal; a second current path from the voltage supply toground, the second path having a second input signal node to which acomplementary input signal is coupled, a second output signal node fromwhich a complementary output signal provided, a second pull-up nodecoupled to the first switching node, and a second switching node coupledto the first pull-up node, the second discharge path coupling thevoltage supply to the second output signal node under control of thesecond pull-up node and coupling the second switching node to ground inresponse to the complementary input signal; and a third current pathfrom the output signal node to ground, the third path coupling theoutput signal node to ground in response to the input signal. 2-38.(canceled)